System of reducing pressures



April 1943- J. 5. ABERCROMBIE 2,316,383

SYSTEM OF REDUCING PRESSURES Filed Dec. 23, 1938 s Sheets-Sheet 1 INVENTOR JANE?) QABERGR A ril 13, 1943. J. 5. ABERCROMBIE 2,316,383

SYSTEM OF REDUCING PRESSURES Filed Dec. 2a, 1938 3 Sheets-Sheet 2 ATTORNEY April 13, 1943.

J. 5.. ABERCROMBIE SYSTEM OF REDUCING PRESSUR-BS Filed Dec. 23, 1938 5 Sheets-Sheet 3 JAMES S. ABERO 0 Patented Apr. 13, 1943 UNITED STATES PATENT OFFICE SYSTEM or REDUCING PRESSURES James S. Abercrombie, Houston, Tex. Application December 23, 1938, Serial No. 247,361

3 Claims.

The invention relates to a system for controlling and reducing pressures, particularly on a well where fluid under pressure is discharging from the well under high pressure and usually contains abrasives,

In completing wells where high pressures are encountered in the producing formation the oil. gas, sand and water may be discharged from the well at high rates of speed and under enormous pressures. It is not uncommon to encounter pressures as high as from 3,000 to 5,000 pounds per square inch. In view of various types of restrictions it is often necessary to confine the production from the well to a predetermined volume and such restriction is usually accomplished by the provision of a choke through which the flow must pass and by which the pressure is reduced.

It is needless to say that such choke even where it is made of a wear resistant material will gradually wear away and become enlarged so that it no longer restricts the flow to the desired amount. Adjustable chokes have been found to be generally unsatisfactory under high pressures.

The present invention contemplates a system of chokes which may be arranged in series so that each choke reduces the pressure a fraction of the entire reduction which is to be accomplished. It is also intended that the system will be so arranged that those chokes which are subjected to the lower pressures can be more readily replaced and the danger of replacing the high pressure chokes can be avoided.

It is one of the objects of the invention to provide a plurality of choke members each of which reduces the pressure and fraction of the whole and wherein the lower pressure chokes may be replaced by chokes each of which assumes a larger fraction of the reduction in pressure in proportion to the amount of Wear which has occurred upon the higher pressure choke.

Still another object of the invention is to provide a well head assembly including high pressure and low pressure chokes so that the low pressure chokes may be replaced in order to compensate for wear on the high pressure chokes so as to extend the period and service to be obtained from the high pressure chokes.

Another object of the invention is to provide in combination with a well head, a flow line assembly and choke system therefor wherein the pressure is stepped down by providing chokes in series so that each choke will accomplish a predetermined pressure reduction.

Still another object of the invention is to provide a choke member with an expansion chamber beyond the choke so as to prevent a sudden expansion due to the reductionin pressure in order to reduce refrigeration.

Other and further objects of the invention will be readily apparent when the following description is considered in connection with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic View of a well head assembly showing the arrangement of the choking system.

Figs. 2 and 3 are end views of the choke shown in Fig. 4,

Fig. 4 is a vertical sectional view of one form of choke and expansion chamber therefor which may be used in practicing the invention.

Fig. 5 is a section of another form of choke.

Fig. 6 is a section on the line G-B of Fig. 5.

In Fig. 1 the production string from the well is indicated at 2 and this string or pipe is usually arranged to be completely closed by a master gate valve 3. Above the valve 3 is a Christmas tree fitting or cross 4 which may have its upper end closed with a bull plug 5 and has the lateral flow line connections 6 and l thereon.

As seen in Fig. 1 a duplicate arrangement of fittings is provided, one upon each side of the well head. Such an arrangement is desired where high pressures are encountered because of the safety factor and may be utilized by flowing one-half of the production through each of the flow line outlets 6 and 'l but the entire production may be passed through either one of the flow lines if it is desired to repair some of the fittings on the alternate line. For purposes of illustration one set of fittings will be described.

To control the flow through the line 6 the valves 9 and I0 are both connected to the fitting 4, one after the other. This duplication of valves is provided so that in event one valve should fail or should the gate member thereof be cut away by the sand in the flow of fluid, the remaining valve would be available to close off the flow.

A T i2 is connected beyond the valve I0 and has connected to one end thereof the choke l5. This choke serves to reduce the pressure and control the volume which may flow therethrough. The valve l6 beyond the choke may be provided so as to close 01? the pressure completely. Beyond the valve IS the T I! carries the branch lines l8 and ii! at each end. The valve 20 in the line 18 and the valve 2| in the line l9 serve to close these branch lines.

Beyond the valves 20 and 2| on each of the branch lines is a T 23 which has a choke 24 connected in the line l8 and the choke 25 in the line l9. A low pressure valve 26 in each of the lines serves to cut ofi the flow of fluid into the discharge pipe 21. A connection 28 between the two branch lines is so arranged that it may accept the flow lfrom either branch line.

The valves 9 and H! are generally known as high pressure valves because they have been constructed and tested to withstand high pressures. The choke l5 tends to reduce the pressure somewhat so that the valves I6, 20 and 2| need not be as expensive valves and they need not be constructed to withstand as high pressures. The choke 24 serves to further reduce the pressure to that which is to flow through the line 21 so that the valve 26 may be a relatively low pressure valve and consequently less expensive.

As an instance in actual practice, say the pressure in the well head 2 is 3200 pounds per square inch and the line pressure at 2'! is to be approximately 200 pounds to the square inch The choke l5 would thus be constructed and proportioned so as to reduce the pressure approximately 1500 pounds. -The choke 24 would also be proportioned to efiect a reduction to approximately 1500 pounds.

Of course a choke is most efiicient and the wear is reduced materially where the pressure drop across the choke is such that the back pressure on the choke is one-half of the applied pressure. As the well-continues to operate the chokes l5 and 24 will of course be subjected to wear. Suppose, therefore that the choke I5 is so worn that instead of effecting a pressure drop of one-half the total drop to be obtained, it only causes a drop of, say 40%. This means that there would be a higher pressure applied to the choke 24 and it would therefore be necessary to replace the choke 24 with a choke having a smaller bore so as to efiect a greater reduction at the choke 24 than is efiected at the choke 15.

It goes without saying that the choke 24 may be more readily replaced than the choke l5 because the pressure which is to be closed off either by the valve [6 or the valve 20 is only approximately one-half of the pressure which would have to be out off by the valves 9 or iii. The fact that sand is being carried by the flow of fluid makes it hazardous to close the valves 9 or ill and quite often a valve is destroyed by having the gate member cut away by the sand when an attempt is made to close the valve. This hazard is not present with the valves IE or 20 because of the lower pressure. The choke 24 may therefore be replaced a considerable number of times depending upon the wear which occurs on the choke l5. If and when the choke l5 becomes so worn that it does not effect any substantial percentage of the reduction in pressure, then the hazard of closing the valves 9 or 10 must be faced and the choke [5 replaced. The service obtained from the high pressure choke under this procedure, however, is'many times that which would ordinarily be obtained and the hazard and expense of replacing the high pressure choke has been avoided.

The flow of the well need not be interrupted in any event, however, when it is desired to change either the chokes l5 or 24 or any of the fittings on either side because the flow can be directed through one side of the assembly while the other side is being repaired. Material reduction in all of the pressures can be effected by flowing one-half of the production through each side of the system and if such were the case, of course the life of the chokes would be materially extended.

It seems clear that the low pressure chokes may be changed at will by inserting smaller chokes so that upon each change the wear which has occurred at the high pressure choke is compensated for so that the desired volume of production at the desired pressure is accomplished.

In Figs. 2, 3 and 4 a choke body 30 has been shown which carries the end flanges 3| and 32.

This body has a central bore 33 which extends through a major portion of the length of the body, and has its inner end defined by a shoulder 34 which merges with a bore 35 of reduced diameter. The end of the bore 33 may be threaded at 36 and the end of the bore 35 may be threaded at 31.

A choke member is illustrated generally at 40 and may be externally threaded at 4! to be engaged by the thread 31. A non-circular opening 42 permits the introduction of a wrench by which a choke may be fixed in position or removed. The choke bore 43 will be of a suitable size, depending upon the conditions encountered.

Particular attention is directed to the inner end of the choke bore 43 where it is flared at 44. The outer end of the choke is beveled at 45 and is arranged to receive a complementary face 46 on the inner end of the expansion sleeve 41. This sleeve 41 is threaded at 48 to be received in the thread 36. The sleeve 41 has an internal tapered bore or chamber 49 which joins the flared portion 44 of the choke member. This forms a continuous passage or chamber which gradually enlarges so as to cause a gradual expansion of h the fluid which is under pressure. This gradual expansion prevents emuisification of the oil, gas and water and avoids undue turbulence and wear upon the parts.

Fig. 5 shows another form of choke with the body 30 having a central bore 50 of uniform diameter and threaded at 5! to receive the sleeve 53 which is quite similar to the sleeve 41 in that it has the tapered chamber 49 and the complementary face 46. Such sleeve has a threaded bore 55 to receive the choke member 40 which is modified slightly to provide a flared portion 56 which is a continuation of the taper 49. The outer end 51 may be made non-circular to facilitate insertion and removal as is the outer end of the internal bore 55 in the sleeve 53. With this construction only one threaded connection is made in the body 30 so that upon expansion or contraction th choke 40 will move with the sleeve 53 and leakage or di-iliculty in replacement avoided.

Broadly the invention contemplates a system of providing a series of chokes, each of which effects a proportionate reduction of the total pressure drop which is to be obtained and wherein the low pressure choke may be replaced to compensate for wear on the high pressure choke.

What is claimed is:

1. A well head assembly comprising in combination a master valve, 9. Christmas tree assem bly thereon including a pair of high pressure flow lines, a pair of valves in each flow line, a high pressure choke in each flow line beyond said valves, a lower pressure valve beyond each high pressure choke, a pair of branch lines beyond each lower pressure valve. a valve in each branch line, a low pressure choke beyond each branch line valve, a low pressure valve beyond each choke, and a pipe line connected to all four of said branch lines beyond said low pressur valves.

2. A well head assembly comprising in combination a master valve, a Christmas tree assembly thereon including a pair of high pressure flow lines, a pair of valves in each flow line, a high pressure choke in each flow line beyond said valves, a lower pressure valv beyond each high pressure choke, a pair of branch lines beyond each lower pressure valve, a valve in each branch line, a low pressure choke beyond each branch line valve, a low pressure valve beyond each choke, and a pipe line connected to all of said branch lines beyond said low pressure valves,

whereby said low pressure chokes may be re-- branch line valve, a still lower pressure valve beyond each choke and a pipe line connected to both of said branch lines beyond said lower pressure valves, whereby said low pressure chokes may be replaced without interrupting the flow thru said high pressure choke.

JAMES S. ABERCROMBIE. 

